Messages in this thread | | | From | Ard Biesheuvel <> | Date | Wed, 8 Jul 2020 15:19:58 +0300 | Subject | Re: [PATCH] arm64/module-plts: Consider the special case where plt_max_entries is 0 |
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On Wed, 8 Jul 2020 at 13:03, 彭浩(Richard) <richard.peng@oppo.com> wrote: > > > On Tue, Jul 07, 2020 at 07:46:08AM -0400, Peng Hao wrote: > >> If plt_max_entries is 0, a warning is triggered. > >> WARNING: CPU: 200 PID: 3000 at arch/arm64/kernel/module-plts.c:97 module_emit_plt_entry+0xa4/0x150 > > > > Which kernel are you seeing this with? There is a PLT-related change in > > for-next/core, and I'd like to rule if out if possible. > > > 5.6.0-rc3+ > >> Signed-off-by: Peng Hao <richard.peng@oppo.com> > >> --- > >> arch/arm64/kernel/module-plts.c | 3 ++- > >> 1 file changed, 2 insertions(+), 1 deletion(-) > >> > >> diff --git a/arch/arm64/kernel/module-plts.c b/arch/arm64/kernel/module-plts.c > >> index 65b08a74aec6..1868c9ac13f2 100644 > >> --- a/arch/arm64/kernel/module-plts.c > >> +++ b/arch/arm64/kernel/module-plts.c > >> @@ -79,7 +79,8 @@ u64 module_emit_plt_entry(struct module *mod, Elf64_Shdr *sechdrs, > >> int i = pltsec->plt_num_entries; > >> int j = i - 1; > >> u64 val = sym->st_value + rela->r_addend; > >> - > >> + if (pltsec->plt_max_entries == 0) > >> + return 0; > > > >Hmm, but if there aren't any PLTs then how do we end up here? > > > We also returned 0 when warning was triggered.
That doesn't really answer the question.
Apparently, you are hitting a R_AARCH64_JUMP26 or R_AARCH64_CALL26 relocation that operates on a b or bl instruction that is more than 128 megabytes away from its target.
In module_frob_arch_sections(), we count all such relocations that point to other sections, and allocate a PLT slot for each (and update plt_max_entries) accordingly. So this means that the relocation in question was disregarded, and this could happen for only two reasons: - the branch instruction and its target are both in the same section, in which case this section is *really* large, - CONFIG_RANDOMIZE_BASE is disabled, but you are still ending up in a situation where the modules are really far away from the core kernel or from other modules.
Do you have a lot of [large] modules loaded when this happens?
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